Biodegradable copolymer containing α-hydroxy acid and α-amino acid units

ABSTRACT

Copolymers designed for use as particulate carriers containing functionalizable amino subunits for coupling with targeting ligand are described. The copolymers are polyesters composed of α-hydroxy acid subunits such as D, L-lactide and α-amino acid subunits such as serine or in the preferred embodiment, terpolymers of D,L-lactide and glycolide and α-amino acid subunits such as serine. Stable vaccine preparations useful as delayed release formulations containing antigen(s) or antigen(s) and co-adjuvants encapsulated within or physically mixed with ploymeric microparticles are described. The particulate carriers are useful for delivering agents to the immune system of a subject by mucosal or parenteral routes to produce immune responses, including antibody responses.

FIELD OF THE INVENTION

The present invention relates to biodegradable microparticles for delivery of a biologically active material and is particularly concerned with such microparticles that are targetable to particular cell types.

BACKGROUND OF THE INVENTION

Vaccines have been used for many years to protect humans and animals against a wide variety of infectious diseases. Such conventional vaccines consist of attenuated pathogens (for example, polio virus), killed pathogens (for example, Bordetella pertussis) or immunogenic components of the pathogen (for example, diphtheria toxoid and hepatitis B surface antigen).

Some antigens are highly immunogenic and are capable alone of eliciting protective immune responses. Other antigens, however, fail to induce a protective immune response or induce only a weak immune response. The immune response of a weakly immunogenic antigen can be significantly enhanced if the antigens are co-administered with adjuvants. Adjuvants enhance the immunogenicity of an antigen but are not necessarily immunogenic themselves. Adjuvants may act by retaining the antigen locally near the site of administration to produce a depot effect facilitating a slow, sustained release of antigen to cells of the immune system. Adjuvants can also attract cells of the immune system to an antigen depot and stimulate such cells to elicit immune responses. Adjuvants have been identified that enhance the immune response to antigens delivered parenterally.

Adjuvants are commonly employed with antigen in vaccine formulations whereby the induction of systemic immunity through parenteral immunization (intramuscular or subcutaneous) is obtained. This approach is suitable for infectious agents gaining access to the body via damaged skin (i.e. Tetanus), however, there are problems encountered due to side-effects and associated toxicity of many adjuvants administered in this fashion. Only those vaccines formulated from aluminum salts (aluminum phosphate or aluminum hydroxide) find routine use in human and veterinary vaccination. However, even these adjuvants are not suitable for use with all antigens and can also cause irritation at the site of injection. There is a clear need to develop adjuvants which safely enhance the immunogenicity of antigens at the site of injection.

There are other problems specific to the nature of the antigen being used. For example most conventional non-living vaccines require multiple doses for effective immunization. Live attenuated vaccines and many nonliving liquid vaccines suffer from the need for controlled storage conditions and are susceptible to inactivation (e.g. thermal sensitivity). There are also problems associated with combining vaccines in single dosage forms, due to adjuvant incompatibilities, pH, buffer type and the presence of salts.

Mucosal immunity is induced primarily by induction of secretory immunoglobulin (sIgA) in intestinal, bronchial or nasal washings and other external secretions. For example parenteral cholera vaccines have been shown to offer limited protection whereas the more recently developed oral form is highly effective (ref. 1--throughout this specification, various references are referred to in parenthesis to more fully describe the state of the art to which this invention pertains. Full bibliographic information for each citation is found at the end of the specification, immediately preceding the claims. The disclosures of these references are hereby incorporated by reference into the present disclosure). Studies with human volunteers have shown that oral administration of influenza vaccine is effective at inducing secretory anti-influenza antibodies in nasal secretions and substances have been identified which might be useful as adjuvants for such ingested vaccines. However, most of these adjuvants are relatively poor in terms of improving immune responses to ingested antigens. Currently, most of these adjuvants have been determined to be safe and efficacious in enhancing immune responses in humans and animals to antigens that are administered via the orogastrointestinal, nasopharyngeal-respiratory and genital tracts or in the ocular orbits. However, administration of antigens via these routes is generally ineffective in eliciting an immune response. Although the above example illustrates the potential of these immunization modes, the development of vaccine formulations for use by these routes has been slow for various reasons. The inability to immunize at the mucosal surface is generally believed to be due to include:

(i) antigen degradation via the acid and/or proteolytic enzymes present during the transit to the mucosal surfaces;

(ii) antigen degradation by secretions presented at the mucosal epithelium;

(iii) limited adsorption across the mucosal epithelium;

(iv) the dilution of the antigen to a concentration that is below that required to induce immune responses; and

(v) ineffective adjuvants and/or delivery systems.

The problems associated with the use of adjuvants in parenteral vaccine formulations and the lack of suitable systems for vaccine delivery to mucosal sites understates the need for new techniques that are effective when administered by various routes and are inherently free from associated toxicity concerns or side-effects.

It is also desired to provide vaccine delivery in a single dosage form for both human and animal immunizations as this has the advantage of reducing time and cost, and in human medicine, increases patient compliance which is of extreme importance in developing countries where access is restricted. This is especially true for infants within these countries.

In order to increase immune responses to administered antigens, a carrier may be used to protect the antigen from degradation and also modulate the uptake of these materials in vivo. Sensitive antigens may be entrapped to protect them against destruction, reduction in immunogenicity or dilution. Methods for formulating a carrier include dispersing an antigen within a polymeric matrix (monolithic matrix) or by the coating of a polymeric material around an antigen to give an outer protective wall (core-shell). The manipulation of the formulation protocol can allow for control over the average size of these materials. This has been shown to be important for the uptake of particulates via oral delivery at specialized M-cells of the Peyers patches within the intestinal tract.

U.S. Pat. No. 5,151,264 describes a particulate carrier of a phospholipid/glycolipid/polysaccharide nature that has been termed Bio Vecteurs Supra Moleculairs (BVSM). The particulate carriers are intended to transport a variety of molecules having biological activity in one of the layers thereof. However, U.S. Pat. No. 5,151,264 does not describe particulate carriers containing antigens for immunization and particularly does not describe particulate carriers for immunization via the orogastrointestinal, nasapharyngeal-respiratory and urogenital tracts and in the ocular orbits or other mucosal sites.

Eldridge et al. (refs 2 and 3) observed the delayed release of antigen in vivo from biodegradable microspheres manufactured from polylactide-co-glycolide copolymer also known as PLG or PLGA. Numerous other polymers have been used to encapsulate antigens for formulation into microparticles and some of these include polyglycolide, polylactide, polycaprolactone, polyanhydrides, polyorthoesters and poly(8-hydroxybutyric acid).

U.S. Pat. No. 5,075,109 describes encapsulation of the antigens trinitrophenylated keyhole limpet hemocyanin and staphylococcal enterotoxin B in 50:50 poly (DL-lactide-co-glycolide). Other polymers for encapsulation are suggested, such as poly(glycolide), poly(DL-lactide-co-glycolide), copolyoxalates, polycaprolactone, poly(lactide-co-caprolactone), poly(esteramides), polyorthoesters and poly(8-hydroxybutyric acid), and poly anhydrides. The encapsulated antigen was administered to mice via gastric intubation and resulted in the appearance of significant antigen-specific IgA antibodies in saliva and gut secretions and in sera. As is stated in this patent, in contrast, the oral administration of the same amount of unencapsulated antigen was ineffective at inducing specific antibodies of any isotype in any of the fluids tested. Poly(DL-lactide-co-glycolide) microcapsules were also used to administer antigen by parenteral injection.

Published PCT application WO 91/06282 describes a delivery vehicle comprising a plurality of bioadhesive microspheres and antigenic vaccine ingredients. The microspheres being of starch, gelatin, dextran, collagen or albumin. This delivery vehicle is particularly intended for the uptake of vaccine across the nasal mucosa. The delivery vehicle may additionally contain an absorption enhancer. The antigens are typically encapsulated within protective polymeric materials.

U.S. Pat. No. 5,571,531 describes particulate carriers comprising a solid matrix of a polysaccharide and a proteinaceous material. A functionalized silicone polymer is bonded to the matrix for the delivery of materials having biological activity.

Although time-delayed release of antigen was shown in the above work, difficulties were encountered when microparticles are manufactured by the described methods. The exposure of biological materials to the organic solvents and physical forces used can lead to denaturation. It may be also be difficult to scale-up the procedures. Furthermore, hydrophilic antigens may be inefficiently encapsulated.

It would be desirable to provide improved carriers without such limitations. It would be particularly desirable to provide polymeric materials which can be formulated into microparticles and microspheres and which contain targetting moieties to target the antigen to preselected ligands. This would have tremendous potential for cells of the immune system.

SUMMARY OF THE INVENTION

The present invention is directed towards the production of a novel and useful polymer that has properties suitable for manufacturing by various processes into microparticles and microspheres. In this invention, modifications of existing processing procedures results in significant improvement in encapsulation efficiencies.

This invention is further directed to the production of useful vaccine delivery systems for antigen(s) or antigen and co-adjuvant cocktails by various immunization routes which include parenteral, oral and intranasal.

In accordance with a first aspect of the invention, there is provided a novel biodegradable, biocompatible polymer having a molecular weight of about 5,000 to about 40,000 daltons and having the general formula: ##STR1## wherein; R₁, R₂, R₃, R₄ and R₅ are selected independently and are selected from H, linear or branched alkyl groups;

R₆ is selected from H, an amine protecting group, a spacer molecule or a biologically active species;

X is selected from an O or S group; and

x and y are integers such that at least about 95% of the polymer is comprised of α-hydroxy acid residues.

The novel polymers are derived by copolymerization of monomers comprising at least one α-hydroxy acid and at least one α-amino acid. The α-hydroxy acids are generally of the formula R₁ R₂ COHCO₂ H, where the R₁ and R₂ groups are H, linear or branched alkyl groups. The α-hydroxy acids may comprise a mixture of α-hydroxy acids, at least one of the mixture of α-hydroxy acids having R₁ and R₂ groups which are hydrogen and another α-hydroxy acid having an R₁ group which is CH₃ and R₂ which is H. The α-amino acids are generally of the formula R₅ CHNHR₆ CO₂ H, where the R₅ group is a hydroxyl methyl or methyl thiol group and R₆ is an amine protecting group.

The amine protecting groups may be carbobenzyloxy, benzyl, paramethoxybenzyl, benzyloxymethoxy, tert-butyloxycarbonyl or [9-fluorenylmethyloxy]carbonyl.

The α-hydroxy acids are generally selected from L-lactic acid, D,L-lactic acid, glycolic acid, hydroxy valeric acid and hydroxybutyric acid.

In a preferred aspect of the invention, the polymers are poly-D,L-lactide-co-glycolide-co-pseudo-Z-serine ester (PLGpZS) and poly-P,L-lactide-co-glycolide-co-pseudo-serine ester (PLGpS).

The polymers may contain biologically active moieties such as cell bioadhesion groups, macrophage stimulators, polyethylene glycol, poly amino acids and/or protected amino acid residues covalently bound to the polymer directly or through side groups.

In the preferred embodiment the bioactive substituents are linked to the polymer via the amino groups on the amino acid moieties directly or via a suitable spacer molecule. The spacer molecule can be selected from α-hydroxy acids represented by the formula R₇ R₈ COHCO₂ H, where R₇ or R₈ groups are independently selected from H, linear or branched alkyl units and α-amino acids represented by the formula R₉ CHNHR₁₀ CO₂ H, where the R₉ group is a hydroxyl methyl or methyl thiol group and R₁₀ is an amine protecting group.

In accordance with another aspect of the present invention, there is provided a process for making a biodegradable, biocompatible polymer of the general formula provided herein which comprises forming a mixture of monomers comprising at least one α-hydroxy acid and at least one α-amino acid with an organic solvent solution of an esterification catalyst under inert atmospheric conditions, copolymerizing the monomers and isolating the resultant polymer. The catalyst used is preferably stannous 2-ethylhexanoate.

The polymer formed by the process can be further deprotected by solid phase catalytic reduction or alternatively by acid catalysis using hydrogen bromide in acetic acid solution.

The process can also further comprise forming the polymer into a film or microparticles.

In accordance with another aspect of this invention, there is provided a particulate carrier for the delivery of biologically active materials to a host, the carrier comprising polymers having a molecular weight of about 5,000 to about 40,000 daltons and having the general formula: ##STR2## wherein; R₁, R₂, R₃, R₄ and R₅ are selected independently and are selected from H, linear or branched alkyl groups;

R₆ is selected from H, an amine protecting group, a spacer molecule or a biologically active species;

X is selected from an O or S group; and

x and y are integers such that at least about 95% of the polymer is comprised of α-hydroxy acid residues.

The particulate carrier generally has a particle size of about 1 to 10 μM.

In a further aspect of the present invention is a process for making a particulate carrier for the delivery of at least one biologically active material to a host, the process comprising;

(a) mixing an organic solvent phase comprising an α-hydroxy acid polymer or copolymer with an aqueous composition comprising dispersed or dissolved biologically active material to form a first water-in-oil emulsion;

(b) dispersing the first water-in-oil emulsion into an aqueous detergent phase to form a second water-in-oil-in-water double emulsion;

(c) removing water from the second double emulsion to form microspheres; and

(d) collecting the microspheres and having the biological material entrapped therein.

The particulate carrier of the present invention can be used as a composition having a biologically active material mixed therewith or entrapped within. The biological materials used may be selected from those which elicit an immune response. Such materials may comprise Haemophilus influenzae proteins, such as a non-proteolytic Hin-47 analog, rD-15, P1, P2, and P6. Other biological material may include proteins (e.g. influenza viral protein), protein mimetics, bacteria, bacterial lysates, viruses (e.g. respiratory syncytial virus), virus-infected cell lysates, DNA plasmids, antisense RNA, peptides (e.g. CLTB-36 and M2), antigens, antibodies, pharmacological agents, antibiotics, carbohydrates, lipids, lipidated amino acids (e.g. tripalmitoyl cysteine), glycolipids, haptens and combinations and mixtures thereof.

The present invention also provides an immunogenic composition comprising the particulate carrier provided herein and a physiologically acceptable carrier therefor. The composition can be administered mucosally or parenterally. The immune response is an antibody response which is a local or serum antibody response. In accordance with this aspect of the invention, there is provided a controlled or delayed release vaccine preparation in stable particulate form and a method of making such a vaccine preparation. Said particles are microspherical and contain a matrix of biodegradable polymer and antigen(s) and/or antigen plus co-adjuvant containing regions.

Advantages of the invention include:

(a) fully biodegradable and biocompatible microparticle formulation;

(b) facilitated antigen presentation to the cells of the immune system resulting in improved antigen immunogenicity;

(c) improved formulating conditions which increase the bioavailability of the antigen.

Additional embodiments of the present invention include the use of the particulate carrier in diagnostic assays and for therapeutic strategies.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be further understood from the following description with reference to the drawings, in which:

FIG. 1 is a schematic showing the ring opening polymerization (ROP) of lactic acid dimer with glycolic acid dimer and N-(carbobenzyloxy)-L-serine lactone with subsequent deprotection in accordance with a preferred aspect of the present invention.

FIG. 2 is a schematic showing the attachment of biologically active moieties to polymer through the side chain of the α-amino acid sub-unit within the polymer. Representative targeting groups include poly-ethylene glycol (PEG) for water solubility and circulation, macrophage stimulators and cell bioadhesion groups. Spacer ligands derived from α-hydroxy acids or α-amino acids may be incorporated to facilitate attachment of the bioactive ligand.

FIG. 3 is a schematic detailing the process used to produce microparticles in accordance with one embodiment of the invention. In this figure, Hin-47 is a non-proteolytic recombinant protein analog derived from Haemophilus influenzae (as described in U.S. Pat. No. 5,506,139), Flu X31 is influenza strain X31 or A-Texas, rD-15 is recombinant protein derived from Haemophilus influenzae (as described in WO 94/12641), PVA=poly vinyl alcohol.

FIG. 4 shows a typical size distribution for poly-D,L-lactide-co-glycolide-co-pseudo-(Z)-serine ester (PLGpZS) and poly-D,L-lactide-co-glycolide-co-pseudo-serine ester (PLGpS) microparticles when prepared in the presence of PBS or a typical protein (non-proteolytic Hin-47 analog) as determined by laser diffraction measurements.

FIG. 5 shows a scanning electron micrograph of microparticles prepared from poly-D,L-lactide-co-glycolide-co-pseudo-(Z)-serine ester (PLGpZS) and poly-D,L-lactide-co-glycolide-co-pseudo-serine ester (PLGpS) in the presence of phosphate buffered saline(PBS).

FIG. 6 shows a scanning electron micrograph of microparticles prepared from poly-D,L-lactide-co-glycolide-co-pseudo-(Z)-serine ester (PLGpZS) and poly-D,L-lactide-co-glycolide-co-pseudo-serine ester (PLGpS) in the presence of a typical antigen/PBS mixture such as Hin-47/PBS.

FIG. 7A shows the in vitro release profile for non-proteolytic Hin-47 analog encapsulated within PLG, PLGpZS and PLGpS microparticles over a three month period obtained from 14 mg samples (typical core loadings range from 2.5 to 5.7 μg protein/mg of microparticles) that were incubated in PBS (pH=7.4) and maintained at 37° C.

FIG. 7B compares the % cumulative release of non-proteolytic Hin-47 analog from PLG, PLGpZS and PLGpS microparticles over a three month period obtained from ˜14 mg samples (typical core loadings range from 2.5 to 5.7 μg protein/mg of microparticles) that were incubated in PBS (pH=7.4) at maintained and 37° C.

FIG. 8A shows the serum IgG responses in mice immunized subcutaneously (S.C.) following various immunization protocols by the 47 kDa membrane protein from Haemophilus influenzae (non-proteolytic Hin-47 analog). Groups of 5 mice were immunized on days 1 and 35 with 250 μL of PBS, pH 7.4, containing either 0.2 or 0.6 μg of non-proteolytic Hin-47 analog incorporated into PLG, PLGpZS or PLGpS microparticles. Sera obtained on days +10, +24, +35, +46 and +60 were evaluated for the presence of anti-Hin-47 IgG antibodies using an enzyme-linked immunosorbent assay (ELISA).

FIG. 8B shows the serum IgG responses in mice immunized subcutaneously (S.C.) following various immunization protocols by the 47 kDa membrane protein from Haemophilus influenzae (non-proteolytic Hin-47 analog). Groups of 5 mice were immunized on days 1 and 35 with 250 μL of PBS, pH 7.4, containing either 0.8 or 2.5 μg of non-proteolytic Hin-47 analog physically mixed with PLG microparticles. Sera obtained on days +10, +24, +35, +46 and +60 were evaluated for the presence of anti-Hin-47 IgG antibodies using an enzyme-linked immunosorbent assay (ELISA).

FIG. 8C shows the serum IgG response subtype profile for pooled bleeds obtained on days +35 and +60 from the study conducted as described in FIGS. 8A and 8B.

FIG. 9A shows the IgG serum antibody responses in mice immunized intragastrically (I.G.) by the 47 kDa membrane protein from Haemophilus influenza (non-proteolytic Hin-47 analog). Groups of 5 mice were immunized on days 1, 7, 14 and 57 with 500 μL of PBS, pH 7.4, containing 4 μg of Hin-47 analog incorporated into PLG, PLGpZS or PLGpS microparticles or physically mixed with PLG, PLGpZS or PLGpS microparticles. Sera obtained on days +13, +35, +56 and +78 were evaluated for the presence of anti-Hin-47 IgG antibodies using an enzyme-linked immunosorbent assay (ELISA).

FIG. 9B shows the serum IgG response subtype profile for pooled bleeds obtained on days +56 and +78 from the study conducted as illustrated in FIG. 9A.

FIG. 9C shows the serum IgA response for the bleed obtained on day +78 from the study conducted as illustrated in FIG. 9A.

FIG. 10A shows the IgG serum antibody responses in mice immunized intranasally (I.N.) by a (1:1) cocktail of the 47 kDa membrane protein from Haemophilus influenzae (non-proteolytic Hin-47 analog) and the 115 kDa membrane protein from Haemophilus influenzae (rD-15). Groups of 5 mice were immunized on days 1, 7, 14 and 57 with 25 μL of PBS, pH 7.4, containing 4 μg of non-proteolytic Hin-47 analog incorporated into PLG, PLGpZS or PLGpS microparticles or physically mixed with PLG, PLGpZS or PLGpS microparticles. Sera obtained on days +13, +35, +56 and +78 were evaluated for the presence of anti-Hin-47 IgG antibodies using an enzyme-linked immunosorbent assay (ELISA).

FIG. 10B shows the serum IgG response subtype profile for pooled bleeds obtained on days +56 and +78 from the study conducted as described in FIG. 10A.

FIG. 10C shows the serum IgA response for the bleed obtained on day +78 from the study conducted as described in FIG. 10A.

FIG. 10D shows the lung lavage IgG response obtained on day +78 from the study conducted as described in FIG. 10A.

FIG. 10E shows the lung lavage sIgA response obtained on day +78 from the study conducted as described in FIG. 10A.

FIG. 11 shows the anti-Flu X31 (i.e. influenza virus type A strain X31) IgG serum antibody responses following various immunization protocols. Groups of 6 mice were immunized subcutaneously (S.C.) on day 1 with 250 μL of PBS, pH 7.4, containing 1.5 μg of HA incorporated into PLG, PLGpZS or PLGpS microparticles. Sera obtained on days +21 and +33 and were evaluated for the presence of anti-Flu X-31 IgG antibodies using an enzyme-linked immunosorbent assay (ELISA).

FIG. 12 shows the anti-Flu X31 (i.e. influenza virus type A strain X31) IgG serum antibody responses following various immunization protocols. Groups of 6 mice were immunized intranasally (I.N.) on days 1 and 34 with 25 μL of PBS, pH 7.4, containing 1.5 μg of HA incorporated into PLG, PLGpZS or PLGpS microparticles. Sera obtained on days +21, +33, +57, +78 and +92 were evaluated for the presence of anti-Flu X-31 IgG antibodies using an enzyme-linked immunosorbent assay (ELISA).

FIG. 13 shows the hemagglutination inhibition antibody assay (i.e. influenza virus strain A-Texas) responses for pooled sera (days +21 and +42) following a single dose subcutaneous administration. Groups of 6 mice were immunized subcutaneously (S.C.) On day 1 with 250 μl of PBS, pH 7.4, containing either 0.35 μg of HA or 3.5 μg of HA incorporated into PLGpS microparticles or 0.35 μg of HA and ˜2 μg of BAY R1-005 or 3.5 μg of HA and ˜20 μg of BAY R1-005 incorporated into PLGpS microparticles or 0.35 μg of HA or 3.5 μg of HA physically mixed with PLGpS microparticles or 0.35 μg of HA and 2 μg of BAY R1-005 or 3.5 μg of HA and 20 μg of BAY R1-005 physically mixed with PLGpS microparticles. Sera obtained on days +21 and +42 were evaluated for the inhibition of hemagglutination of erythrocytes.

DETAILED DESCRIPTION OF THE INVENTION

The novel polymers of the present invention are biocompatible, degradable to benign metabolites which may be present in the body and may possess biologically active moieties, such as cell bioadhesion groups, macrophage stimulators, poly amino acids and polyethylene glycol coupled to the polymer via at least one spacer molecule selected from α-hydroxy acids and α-amino acids. As such, the novel polymers possess functionality.

Methods are also described for the synthesis of polymers having advantageous properties for processing into microparticles containing biologically active materials and for which chemical modification with biologically active targeting groups is possible.

In the preferred embodiments, the copolymers are produced by the polymerization of α-hydroxy acids with pseudo α-amino acids and terpolymers produced by the polymerization of two α-hydroxy acids with pseudo-α-amino acids. The copolymer or terpolymer may then be derivatised with biologically active targeting ligands via the amino acid subunit by covalently coupling with the free amino group directly or subsequent to further derivatization with a suitable spacer ligand.

Amino Acid Monomer Synthesis

In general an N-protected serine (or cysteine) is cyclized via a Mitsunobu reaction (ref. 5) to give a four membered lactone (or thiolactone).

This transformation gives rise to an ester (or thioester) linkage. It is important to have protection on the amine portion of the amino acid precursor that is compatible with the reaction conditions. Preferentially the carbobenzyloxy (CBZ or Z) group is used although other suitable functionalities such as benzyl (Bn), para-methoxybenzyl (MeOBn) benzyloxymethoxy (BOM), tert-butyloxycarbonyl (t-BOC) or [9-fluorenylmethyl) oxy]carbonyl (FMOC) may be employed.

The synthesis of the N-Z-L-Serine β-Lactone monomer was based on a modified procedure from the literature (ref. 6).

Copolymerization Of α-Hydroxy Acid And Amino Acid Containing Monomers and Functionalization of Amino Acid Sidechains

Two methods are applicable for copolymerization of α-hydroxy acid monomers. Polymerization via polycondensation or from the melt (bulk polymerization) are possible alternatives.

It has been long known that condensation polymerizations are problematic as relatively low molecular weight materials often result with competing side reactions commonly giving rise to unwanted byproducts (refs. 7 and 8).

However ring opening polymerization (ROP) of the cyclic dimers of α-hydroxy acids such as glycolide and lactide from the bulk phase was shown to proceed readily in the presence of a variety of catalysts to give polymers of high molecular weights with stannous octoate being preferred (refs. 9-15).

There are numerous methods for preparing poly(amino acids)(refs. 16, 17 and 18) or pseudopoly (amino acids) (refs. 6 and 19).

The noted biodegradable properties of poly-α-hydroxy acids (in particular those of 50:50 D,L-lactide and glycolide) and poly(amino acids) has resulted in increased efforts to develop methods for incorporating amino acids into the backbone of α-hydroxy acid polymers (refs. 20-25).

Advances have been made in producing copolyesteramides containing α-hydroxy acid sub-units such as lactide or glycolide and α-amino acid sub-units such as glycine or lysine (refs. 22, 23 and 26).

The degradation rate of the biodegradable polymer and the release rates of encapsulated materials from homopolymers of glycolide, lactide or from copolymers of these materials has been shown to be strongly influenced by their molecular weight and structure such as degree of crystallinity and relative hydrophobicity or hydrophilicity. Specifically, microspheres formulated from higher molecular weight polymers derived from α-hydroxy acids degrade over longer periods of time than lower molecular weight analogs. Similarly highly crystalline materials erode at rates much slower than amorphous analogs. This is related to the accessibility of water to the hydrolytically unstable ester linkages (ref. 27).

It has been established that random amorphous copolymers composed of 50% D,L-lactide and 50% glycolide exhibit the most advanced degradation rates (refs. 2 and 3) with 50% by weight remaining after approximately 6 weeks, when immersed in PBS buffer (pH=7.4).

The copolyesteramides described above are semi-crystalline materials which may suffer from prolonged retention at the site of administration long after the encapsulated materials are fully released.

Since it would be advantageous to have a polymer that has degraded at or near the point when the encapsulated material has been fully released, we developed methods for randomly incorporating equal amounts of D,L-lactide and glycolide into a terpolymer which also contained α-amino acid sub-units. A terpolymer of relatively moderate molecular weight was used to ensure the amorphous terpolymer would retain sufficient mechanical strength for processing into films and microparticles yet exhibit satisfactory polymer degradation and release rates for entrapped materials.

The N-protected-L-serine lactone contains an ester bond which may be polymerized via transesterification catalysts (ref. 6). Additionally it has been shown that six-membered ring lactones such as lactide and glycolide can be copolymerized with four-membered ring propiolactones by use of insertion/coordination type catalysts/initiators (ref. 13). It was expected that efficient transesterification catalysts such as those derived from Sn reagents would be required if relatively sufficient reactivity of all monomer units was to be achieved.

We used the copolymerization of glycolide, D,L-lactide and N-Z-L-serine lactone mediated by stannous octoate. Deprotection of the CBZ group of the copolymer or terpolymer can be achieved by various methods. Solid phase catalytic reduction or acid catalysis (ref. 27) are two possibilities (FIG. 1).

The resultant copolymer or terpolymer can be further elaborated with targeting moieties such as cell adhesion epitopes, poly ethylene glycol (PEG) ligands for circulation, macrophage stimulators and poly amino acid grafts as depicted in FIG. 2. A spacer unit may be incorporated for example, α-hydroxy acid or an α-amino acid unit, and may be readily derivatised with the appropriate targeting units. The polymer so formed has a molecular weight of from about 5,000 to about 40,000 daltons.

Microparticle Formation

The term "microparticle" as used herein refers to any particulate carrier greater than 1 micron in size which is used for the delivery of biologically active materials. The term "microsphere" as used herein refers to a microparticle containing one or more active ingredients (e.g. antigens, adjuvants, plasmid DNA).

A flow diagram illustrating the process of microparticle formation as described herein is shown in FIG. 3. In general the copolymer (PLG, PLGpZS or PLGpS) is solubilized solely or with additional excipients present in a compatible solvent such as dichloromethane, ethyl acetate, acetone or mixtures thereof. Excipients included in the formulation such as sucrose, mannose, trehalose or gelatin serve as cryoprotectants or lyoprotectants. Other materials possessing known adjuvancy such as BAY R1-005 (BAY) (ref. 29) or tripalmitoyl cysteine (TPC) (ref. 30) have been included during formulation.

A 1% to 2% copolymer solution of total volume 12 mL is preferably prepared. To this solution is added 800 μL of phosphate buffered saline (PBS) or 800 μL of antigen solution (concentration typically from 1 to 2 mg/mL) in PBS or other stabilizing buffers which may contain additional excipients. This mixture is then homogenized to form a water in oil emulsion. Once formed this mixture is dispersed into 100 mL of a 0.5% to 10.0% aqueous solution containing non-ionic emulsion stabilizers such as poly vinyl alcohol (PVA), methyl cellulose or Triton X-100. This mixture is immediately homogenized to form a water in oil in water double emulsion. The average size and polydispersity of the resultant droplets can be conveniently measured through use of the Coulter LS-100 light scattering detector. Typical size distributions when PBS or Antigen/PBS mixtures are encapsulated range from 1 to 20 microns (with the majority less than 10 microns in size). The solvent is then slowly removed via evaporation with gentle warming to harden the incipient microspheres. Once the solvent is removed the mixture is centrifuged to collect the microspheres and repeatedly washed with deionized water to ensure complete removal of residual emulsion stabilizers. The microspheres are then frozen in a dry ice/acetone bath and lyophilized overnight to yield a white freely flowing powder of microspheres (typically 1.0 to 12 microns in size as determined by light scattering measurements and directly verified via scanning electron micrography).

It is clearly apparent to one skilled in the art, that the various embodiments of the present invention have many applications in the fields of medicine and in particular vaccination, diagnosis and treatment of infections with pathogens including bacteria and viruses. A further non-limiting discussion of such uses is presented below.

Vaccine Preparation

In an embodiment, immunogenic compositions, suitable to be used as, for example, vaccines, may be prepared from microparticles as disclosed herein. The immunogenic composition containing a biologically active immunogenic material can elicit an immune response by the host to which it has been administered including the production of antibodies by the host.

The immunogenic composition may be prepared as injectables, as liquid solutions or emulsions. The microparticles may be mixed with physiologically acceptable excipients which are compatible with the microparticles. These may include, water, saline, dextrose, glycerol, ethanol and combinations thereof. The vaccine may further contain additional substances such as wetting or emulsifying agents, pH buffering agents, or adjuvants to further enhance the effectiveness of the vaccines. Vaccines may be administered parenterally, by injection subcutaneously or intramuscularly.

Alternatively, the immunogenic compositions comprising microparticles formed according to the present invention may be delivered in a manner to elicit an immune response at mucosal surfaces. Thus, the immunogenic composition may be administered to mucosal surfaces by nasal, oral (intragastric), buccal or rectal routes. Oral formulations may include normally employed incipients, such as pharmaceutical grades of saccharin, cellulose and magnesium carbonate.

These compositions may take the form of solutions, suspensions, tablets, pills, capsules, sustained release formulations or powders. In order to protect the microparticles and the encapsulated material contained within the core of the microparticle or which is physically mixed with the microparticles, from gastric acidity when administered by the oral route, an acidic neutralizing preparation (such as a sodium bicarbonate preparation) is advantageously administered before, concomitant with or directly after administration of the microparticles.

The vaccines are administered in a manner compatible with the dosage formulation, and in such amount as to be therapeutically effective, protective and immunogenic. The quantity to be administered depends on the subject to be treated, including, for example, the capacity of the subject's immune system to synthesize antibodies, and if needed, to produce a cell-mediated immune response. Precise amounts of microparticle and material having biological activity required to be administered depend on the judgement of the practitioner. However, suitable dosage ranges are readily determinable by one skilled in the art and may be of the order of micrograms to milligrams. Suitable regimes for initial administration and booster doses are also variable, but may include an initial administration followed by subsequent administrations. The dosage of the vaccine may also depend on the route of administration and thus vary from one host to another.

The polymers of the present invention as applied to vaccine formulations, are also useful for new vaccine strategies such as with the use of DNA or antisense RNA. As microparticle carriers, the polymers of the present invention can be prepared to contain DNA coding for a gene or genes for an antigenic portion of a virus such as the core protein or the envelope protein. As the DNA is released from the carrier, the host cells take up the foreign DNA, express the gene of interest and make the corresponding viral protein inside the cell. Advantageously, the viral protein enters the cells major histocompatibility complex pathway which evokes cell-mediated immunity. Standard vaccine antigens in comparison, are taken up into cells and processed through the MHC class II system which stimulates antibody responses.

The DNA may be in the form of naked DNA which is free of all associated proteins and which does not require a complex vector system. The desired gene may be inserted into a vector, such as a plasmid, encapsulated within the microparticle herein described, and injected into the tissues of a mammal which expresses the gene product and evokes an immune response.

Antisense oligonucleotides can also be used in conjunction with the polymers of the present invention. Nucleic acid sequences may be designed to bind to a specific corresponding mRNA sequence for a known protein to inhibit the production of the protein. The microparticles described herein, can be used to deliver such antisense nucleotides (oligonucleotides or expressed nucleotides) as a therapeutic strategy for the treatment of various immunological diseases as well as hypertension, cardiovascular disease and cancer.

The slow-release characteristic of the polymer microparticles developed herein also has use in the field of pharmacology where the microparticles can be used to deliver pharmacological agents in a slow and continual manner. A wide range of drugs such as anti-hypertensives, analgesics, steroids and antibiotics can be used in accordance with the present invention to provide a slow release drug delivery system.

The polymer in the form of a film having a biological agent entrapped or physically admixed thereto, may also have use as a coating for surgical implants and devices. For example, the polymer as a film having antibiotic incorporated therein can be used to coat surgically implanted catheters in order to provide continual slow-release of antibiotics to combat infection.

The microparticle carrier may also be useful as a diagnostic agent. Together with the appropriate antibody, imaging agents can be incorporated with the microparticles. In this manner diseased tissues can be targeted and imaged in order to identify or monitor the clinical course of a disease.

The polymers, as microparticles, also have use in diagnostic kits when used in conjunction with appropriate antibodies.

EXAMPLES

The above disclosure generally describes the present invention. A more complete understanding can be obtained by reference to the following specific Examples. These Examples are described solely for purposes of illustration and are not intended to limit the scope of the invention. Changes in the form and substitution of equivalents are contemplated as circumstances may suggest or render expedient. Although specific terms have been employed herein, such terms are intended in a descriptive sense and not for purposes of limitations.

Methods of chemistry, organic chemistry, polymer chemistry, protein biochemistry and immunology used but not explicitly described in this disclosure and these Examples are amply reported in the scientific literature and are well within the ability of those skilled in the art.

Example 1

This Example illustrates the preparation of N-Z-L-Serine β-Lactone.

The preparation of this cyclic N-protected amino acid lactone was based on a modified procedure in which an N-protected-α-amino acid is reacted to yield cyclized pseudo-α-amino acid monomer (ref. 6). All glassware was pre-dried overnight in an oven set at 120° C. Prior to use it was cooled in a vacuum desiccator and purged under a stream of dry nitrogen for 10 minutes.

To a 1L three necked round bottomed flask under nitrogen was added triphenylphosphine (TPP; Aldrich; 7.87 mL; 50 mmol; FW: 174.16). To this was added 200 mL of anhydrous acetonitrile (CH₃ CN; Aldrich): anhydrous tetrahydrofuran (THF; Aldrich) solution (volume ratio 85:15) via syringe and stirred until the solid TPP was dissolved. To this solution diethyl azodicarboxylate (DEAD; Aldrich; 7.87 mL; 50 mmol; FW: 262.29) was added via syringe and the solution stirred at room temperature for 30 minutes. The solution was then cooled to about -45° C. to -48° C. by immersing the reaction vessel in an acetonitrile/dry ice bath. Once the internal temperature of the solution reached about -45° C., a solution of N-Carbobenzyloxy-L-Serine (N-CBZ-L-Serine; Sigma; 11.94 g; 49.8 mmol; FW: 239.2) in 200 mL of anhydrous CH₃ CN:THF (volume ratio 85:15) was slowly added via dropping funnel over a period of 1 hour. The temperature of the solution was maintained at about -45° C. during the addition and allowed to slowly warm to room temperature once the addition was complete with continuous stirring overnight. This reaction results in the formation of an ester bond between the serine hydroxyl side chain and the carboxylic acid in the presence of the CBZ protected α-amino group.

Upon completion of the reaction the solvents were removed via evaporation (35° C. to 45° C.). This yields a yellow oil/slurry (˜35 g). To this slurry was added 50 mL of dichloromethane:ethyl acetate (volume ratio 85:15) solution which results in the precipitation of 1,2-dicarbethoxyhydrazine byproduct. This material was removed by filtration under vacuum followed by solvent removal via evaporation. The above procedure can be repeated to further remove residual byproducts. The waxy solid crude material was then purified via silica gel column chromatography with eluent 85:15 dichloromethane:ethyl acetate as solvent. The product serine lactone can be identified via thin layer chromatography as this material has an R_(f) of 0.75 on silica plates eluted with 85:15 dichloromethane:ethyl acetate when stained with a 1M H₂ SO₄ solution and is also UV visible. The product was recrystallized from ethyl acetate:hexane (˜1L), filtered and dried in vacuo.

A clean white solid is obtained in 40% yield after recrystallization with a melting point (Tm=133-134° C.) and all other physical parameters (NMR, IR, mass spectroscopy, elemental analysis) conforming to that previously demonstrated (ref. 6).

Example 2

This Example illustrates the preparation of the copolymer poly-D,L-Lactide-co-Glycolide-co-pseudo-Z-Serine Ester (PLGpZS) as shown in FIG. 1.

Glassware was pre-dried overnight. Prior to use it was cooled in a vacuum desiccator. Additionally the polymerization vessel (glass ampule) must be siliconized (SurfaSil; Pierce; 2% solution in toluene) and all transfer reactions and additions of reagents and monomers to polymerization vessel must be conducted in a glove box maintained under a dry nitrogen environment.

Prior to polymerization the D,L-lactide (2,6-dimethyl-1,4-dioxane-2,5-dione; Aldrich; FW: 144.13) and glycolide (Boehringer Ingelheim; FW: 116.096) was recrystallized from anhydrous ethyl acetate in the glove box and dried in vacuo for about 2 days. Once fully dried the monomers can be stored in the glove box with the freshly recrystallized serine lactone (stored at 0° C.) of Example 1 brought directly into the glove box. All monomers and catalyst/initiators were weighed and transferred to glass ampules within the glove box.

The total combined mass of monomer transferred to the ampoule typically ranges from 1 g to 5 g with the molar ratio of D,L-lactide:glycolide:serine lactone ranging from 42.5:42.5:15.0 to 49.0:49.0:2.0. A molar ratio of D,L-lactide:glycolide:serine lactone of 47.5:47.5:5.0 was used in the preferred embodiment. A stock solution of catalyst (stannous 2-ethlyhexanoate (Sn(Oct)₂ ; Sigma; FW 405.1, 1.25 g/mL) in anhydrous chloroform (Aldrich) was prepared in the glove box and added via microsyringe to the glass ampule (molar ratio of catalyst to monomer=1/1000). A stir bar was also placed in the ampule. A greased ground glass joint valve was placed on the ampule to preserve the inert environment during removal from the glove box. The ampule was then directly placed on a vacuum line with slow removal of chloroform by evaporation. The ampules were then placed in an oil bath at ca. 120° C. to bring all reagents into the melt followed by flame sealing and placement in a thermoregulated oven at 120° C. for 28 hours. After reaction the ampules are quenched by placing in liquid nitrogen and stored at -20° C. until further work up. The ampule was cracked and crude polymer recovered by dissolving in chloroform. The solvent was removed by evaporation and crude polymer dried in vacuo to give an amber crystalline material (yield 80% to 90%).

The polymer was purified by dissolving in chloroform, filtering off insoluble material and precipitating into hexane (Aldrich). The polymer was recovered by filtration and this procedure was repeated to ensure the complete removal of unreacted monomer. The polymer was dried in vacuo for about 2 days to give a clean white powder in 30% to 35% overall yield after second precipitation. The molecular weight of this material was dependent on reaction time with typical values of Mw=17,000-22,000, Mn=6,500-8,000. Differential scanning calorimetry (DSC) analysis indicates a single transition indicative of a random amorphous polymer. Glass transitions (Tg) range from 39° C. to 43° C. dependent on the molecular weight of the material obtained. The serine content of the polymer was determined by amino acid analysis (AAA) diagnostic for the phenylthio isocyanate serine derivative obtained by hydrolysis of the polymer, ¹ H NMR (integration of aromatic residues of the CBZ protecting group on serine relative to the glycolide and D,L-lactide sub-units) and elemental analysis (nitrogen present only in the side chain of serine). The AAA analysis typically indicated 1.7% to 2.1% serine content with the ¹ H NMR analysis indicating 2.0% to 2.5% and the elemental analysis indicating 2.4% to 3.4% serine respectively. IR analysis of the polymer was diagnostic for the presence of ester, carbamate and hydroxyl groups.

¹ H NMR also allowed for the determination of the relative incorporation efficiencies of all monomer components under the stated reaction conditions. Typical ratios of D,L-lactide:glycolide:Z-serine found in purified polymer are reproducibly 52.0% to 54.0% D,L-lactide, 41.0% to 43.5% glycolide and 2.0% to 2.5% Z-serine respectively.

¹ H NMR and ¹³ C NMR signal intensities for resonances unique to glycolide or D,L-lactide are well resolved from each other and sensitive to sequence effects. From the observed patterns a random sequence distribution is supported.

Example 3

This Example illustrates the preparation of the copolymer poly-D,L-Lactide-co-Glycolide-co-pseudo-Serine Ester (PLGpS) as shown in FIG. 1.

All glassware was pre-dried overnight. Prior to use it was cooled in a vacuum desiccator and purged under a stream of dry nitrogen for 10 minutes. All reactions were conducted under inert atmosphere of dry nitrogen.

To a 2 necked 100 mL round bottomed flask equipped with a stir bar was placed 400 mg of polymer (PLGpZS). To this was added a 10 mL solution of 30% hydrogen bromide in acetic acid (Aldrich; FW: 80.92) which was sufficient for slurry formation. The slurry was stirred for 30 to 45 minutes and quenched by dropwise addition of anhydrous diethyl ether (Aldrich) followed by anhydrous methanol (Aldrich). This results in polymer precipitation which was then isolated by vacuum filtration. The crude polymer precipitate was washed with diethyl ether and reprecipitated from chloroform:hexane. The purified polymer was dried in vacuo for about 2 days to give a clean white powder in 50% to 60% overall yield. The molecular weight ranged from Mw=15,000-18,000, Mn=5,000-6,500. The rate of deprotection of the CBZ group is faster than the competitive cleavage of the ester backbone with HBr/Acetic acid. However, under these conditions there is broadening of the molecular weight distribution and reduction in the molecular weight of the product as a consequence of using this reagent. This trend can be reduced by conducting the reaction for shorter time intervals or eliminated by removing the protecting group via hydrogenation using hydrogen in the presence of palladium on charcoal. DSC analysis indicates a single transition indicative of a random amorphous polymer. Glass transitions (Tg) range from 42° C. to 45° C. depending on the molecular weight of the material obtained. The serine content of the polymer was determined by amino acid analysis (AAA) diagnostic for the phenylthio isocyanate serine derivative obtained by hydrolysis of the polymer and elemental analysis (nitrogen present only in the side chain of serine). The AAA analysis typically indicated 1.4% to 1.7% serine content and the elemental analysis indicating 2.0% to 2.7% serine respectively. IR analysis of the polymer was diagnostic for the presence of ester, amine and hydroxyl groups.

¹ H NMR for residual protected polymer indicated that greater than 90% of the N-carbobenzyloxy groups were successfully removed. With shorter reaction times the extent of deprotection is concomitantly reduced. Typical ratios of D,L-lactide:glycolide:Z-serine:serine found in purified polymer are reproducibly 53.0% to 55.0% D,L-lactide, 40.0% to 43.0% glycolide, 0.15% to 0.25% Z-serine and 1.7% to 2.1% serine respectively.

Example 4

This Example illustrates the production of a film from the copolymers synthesized in Examples 2 and 3.

To produce the film, 50 mg of poly-D,L-Lactide-co-Glycolide (PLG) (Mw=31,000), poly-D,L-Lactide-co-Glycolide-co-pseudo-Z-Serine Ester (PLGpZS) (Mw=20,000) or poly-D,L-Lactide-co-Glycolide-co-pseudo-Serine Ester (PLGpS) (Mw=19,000) was weighed out and placed in a 10 mL beaker. Anhydrous chloroform (1 mL) was added to dissolve the copolymer. This solution was filtered and added dropwise to a microscope slide placed in a petri dish. The petri dish was then covered with a 250 mL beaker to ensure slow evaporation over 48 hours. The resultant films were translucent and contact angle measurements performed using a goniometer gave average values of 75° for PLG, 75° for PLGpZS and 68.2° for PLGpS respectively. Thus the PLG and PLGpZS copolymers are of comparable hydrophobicity with the PLGpS copolymer proving to be slightly more hydrophilic and of higher surface energy.

Example 5

This Example illustrates the process of microparticle formation encapsulating PBS or antigen/PBS (microsphere formation).

A flow diagram illustrating the process of microparticle formation as described herein is shown in FIG. 3.

Specifically, 100 mg of copolymer was added to 12 mL of dichloromethane. To this was added 800 μL of phosphate buffered saline (PBS) solution or 800 μL of non-proteolytic Hin-47 analog(concentration typically from 1 to 2 mg/mL) in PBS. This mixture was then homogenized (20 seconds at 6,000 rpm). Once formed this mixture was dispersed into 100 mL of a 1.0% aqueous solution of poly vinyl alcohol (PVA) and immediately homogenized (40 seconds at 8,000 rpm) to form a water in oil in water double emulsion. Typical size distributions when PBS or a typical antigen (Hin-47/PBS) is used as encapsulant are depicted in FIG. 4. Polydisperse microparticles (with the majority less than 10 microns in size) are formed under these conditions. The solvent was then slowly removed via evaporation and the microspheres collected by centrifugation. The particles were washed (5×) with deionized water and then frozen in a dry ice/acetone bath and lyophilized overnight to yield a white freely flowing powder of microspheres (typically 1.5 to 10 microns in size as determined by light scattering measurements and directly verified via scanning electron micrography). A representative scanning electron micrograph for PLGpZS or PLGpS microspheres encapsulating PBS is shown in FIG. 5. A representative scanning electron micrograph for PLGpZS or PLGpS microspheres encapsulating a typical antigen (non-proteolytic Hin-47 analog) in PBS is shown in FIG. 6.

By the method stated above microparticles containing several different antigen(s) and/or antigen(s)+adjuvant have been prepared (see Table 1).

Example 6

This Example illustrates the microparticle core loading efficiency and antigen epitope recovery from such microparticles.

Two variations of the same method were employed to determine the antigen content or "core loading" of the microparticles isolated. Amino acid analysis was performed on the hydrosylates of microparticles obtained by either acid hydrolysis (6M HCl) of the solid particles or by base/SDS hydrolysis (0.1N NaOH/1% SDS) followed by neutralization with 0.1N HCl. Alternatively, the solid microspheres can be dissolved in DMSO a compatible solvent solubilizing both polymer and protein and amino acid analysis performed directly on the lyophilized sample. The acid or base mediated hydrolysis proved to be the preferred method giving the most reproducible results (+/- 5%). Where available a validated Enzyme Linked Immunosorbant Assay (ELISA) polyclonal assay was performed on the hydrosylates to determine the epitope equivalence.

Specifically, for the quantitation of non-proteolytic Hin-47 analog antigen by ELISA the non-proteolytic Hin-47 analog antigen is captured on affinity purified guinea pig anti-Hin47 coated microtitre wells (Add 50 μL of a 2 μg/mL solution of non-proteolytic Hin-47 analog antigen per well), which have been blocked with 5% skim milk in PBS. The antigen present is detected by an affinity purified rabbit anti-Hin-47 followed by horse radish peroxidase F(abs)2, donkey anti-rabbit IgG. To develop the color of this reaction 100 μL of the substrate H₂ O₂ (9 parts) in the presence of tetramethylbenzidine (TMB) (1 part), and the reaction progress terminated by addition of 50 μL of a 2M sulphuric acid solution to each well. The intensity of the color (read at 450 nm) is directly proportional to the amount of non-proteolytic Hin-47 analog in the well. The concentration of non-proteolytic Hin-47 analog in each test sample is derived by extrapolation from a standard curve which is obtained by multiple dilutions of a reference sample. All samples were analyzed in duplicate.

The amino acid analysis for core loading and Hin-47 specific polyclonal ELISA analysis of epitope recovery for microparticles encapsulating non-proteolytic Hin-47 analog or non-proteolytic Hin-47 analog plus BAY R1-005 within PLG, PLGpZS and PLGpS copolymers is shown in Table 2. The core loadings for microparticles prepared solely from Hin-47 range from 20% to 43% with from 10% to 31% of the epitope preserved during formulation. The core loadings for microparticles prepared from non-proteolytic Hin-47 analog in the presence of BAY R1-005 range from 26% to 59% (an absolute increase of 6% to 16%) with from 20% to 39% (an absolute increase of 4% to 18%) of the epitope preserved during formulation. Thus formulation in the presence of BAY R1-005 concomitantly increases the loading efficiency and serves to protect the epitope.

The amino acid analysis of core loading for microparticles encapsulating rD-15 within PLG, PLGpZS and PLGpS copolymers is shown in Table 3. Core loadings ranging from 39% to 44% were obtained. This protein is membrane derived and thus more hydrophobic than the non-proteolytic Hin-47 analog of the previous example. Increased encapsulation efficiencies relative to non-proteolytic Hin-47 analog of Example 10 were routinely observed when using this antigen.

The amino acid analysis for core loading and epitope recovery for microparticles encapsulating a cocktail of non-proteolytic Hin-47 analog and rD-15 (1:1 cocktail) within PLG, PLGpZS and PLGpS copolymers is shown in Table 3. It was expected that coencapsulation of non-proteolytic Hin-47 analog in the presence of rD-15 would result in higher overall loading efficiencies. Core loadings ranging from 35% to 62% were obtained with from 8% to 26% of the non-proteolytic Hin-47 analog epitope preserved during formulation. The overall loading efficiency of the more hydrophilic component (non-proteolytic Hin-47 analog) was increased by coencapsulation with rD-15 when formulated with PLGpZS or PLGpS copolymers. This effect was not observed when PLG was used. Irrespective of copolymer formulation similar non-proteolytic Hin-47 analog epitope recovery as compared with example 10 was obtained.

The amino acid analysis of core loading for microparticles encapsulating Flu X-31 or Flu X-31 and BAY R1-005 within PLG, PLGpZS and PLGpS copolymers is shown in Table 4. Core loadings ranging from 26% to 40% were obtained with Flu X-31 and for Flu X-31 in the presence of BAY R1-005 core loadings ranging from 31% to 53% were obtained. Thus an absolute increase of 5% to 13% was obtained when formulating in the presence of BAY R1-005. The only exception was the formulation of Flu X-31 with BAY R1-005 and PLGpS where an absolute decrease of 9% was observed.

A core loading of 21% for PLGpS microparticles encapsulating Flu A-Texas was obtained. For PLGpS microparticles encapsulating Flu A-Texas in the presence of BAY R1-005 a core loading of 32% was obtained.

When a different strain of Flu was employed (A-Texas) with BAY R1-005 and PLGpS copolymer the tendency to increase the encapsulation efficiency was once again observed. When formulating PLGpS with Flu A-Texas in the presence of BAY R1-005 an absolute increase of 11% was obtained. This suggests that the formulation for PLGpS and proteins in the presence of BAY R1-005 must be optimized in each case. As in Example 10, the addition of the coadjuvant BAY R1-005 has resulted in higher loading efficiencies.

Example 7

This Example illustrates the in vitro release rates and total cumulative % recovery of protein for a model antigen (non-proteolytic Hin-47 analog) encapsulated within PLG (used as a control for comparison purposes) and synthesized copolymers PLGpZS and PLGpS.

The PLG formulated into microspheres containing antigen was determined to be of molecular weight; Mw=26,000 with a 50:50 ratio of D,L-Lactide:Glycolide. This material is of similar constitution and molecular weight to that obtained for copolymers PLGpZS and PLGpS of examples 2 and 3. In a typical experiment 14 mg of microspheres (core loading of non-proteolytic Hin-47 analog for PLG=2.8 μg/mg, PLGpZS=5.7 μg/mg and PLGpS=2.5 μg/mg as determined by amino acid analysis of the microsphere hydrosylates) was placed in a 2 mL eppendorf tube to which was added 1.0 mL of PBS (pH=7.4). The tube was then placed in a thermoregulated oven maintained at 37° C. without agitation. At various time intervals the PBS solution was extracted and analyzed for total protein via amino acid analysis. After each extraction the PBS solution was replaced with continued sampling to a maximum of 90 days. In control experiments the majority of the microspheres (>80% by weight) prepared from PLG or PLGpS copolymers were consumed by day 45. The degradation of microspheres formulated from PLGpZS copolymers was observed to be somewhat slower requiring 60 days to erode to essentially the same extent.

Similar antigen release trends were observed with each group of microparticles wherein small amounts of protein is released over the first few days. This diminishes to near undetectable limits up to day 14 whereafter the protein release rate steadily increases to a maximum at about day 30. Subsequent to this the release of protein falls to levels again approaching the limit of detection. The total % cumulative recovery of protein from these samples ranged from 40% to 65% relative to the respective core loadings of each group of microspheres.

FIG. 7A illustrates this release rate at specific time points for each sample and FIG. 7B shows the % cumulative release for each sample examined. It is evident that under these conditions the best recovery of protein from microspheres follows the order PLGpS>PLG>PLGpZS although the core loading for the PLGpZS microparticles was approximately twice that of the PLG or PLGpS analogs and this may influence the release rate. In addition this matrix has been shown to degrade at a slower rate and thus there may be residual material within the microparticles. Evidence for this can be seen in FIG. 7B whereby a marginal increase in protein recovery is observed from day 60 to day 90 for PLGpZS microparticles. Over this same time interval protein recovered from PLG or PLGpS microparticles is essentially non-existent.

In control experiments, supernatant solutions of PBS obtained from periodic extractions of PBS loaded PLG, PLGpZS or PLGpS microparticles incubated at 37° C. were monitored for pH changes. It is known that the erosion process for PLGA matrices is accompanied by changes in the pH microenvironment within the microparticle. This can have a serious effect on protein stability as pH induced conformational changes can ensue as a consequence of these changes. An indication of the magnitude of these changes can be obtained by monitoring the pH of the surrounding medium. We have found that incorporation of small percentages of amino acid sub-units within the copolymer can retard this process. This may be of importance during the release phase for proteins sensitive to acidic pH. Specifically when incubating ˜10 mg of microparticles in 1.2 mL of PBS buffer (pH=7.4) it required approximately 16 days for supernatant extractions of PLG (Mw=26,000 daltons) to fall below pH 5.0. By analogy the pH of supernatant extractions obtained from PLGpZS (Mw=20,000 daltons, ˜2.0% serine incorporated), or PLGpS (Mw=18,000 daltons, 1.7% serine incorporated) was determined to be approximately 5.5 to 6.2 respectively. The degradation rates for PLG and PLGpS examined in this study were similar (as measured by mass loss of matrix) whereas the PLGpS matrix degraded at a reduced rate.

Thus the in vitro release study demonstrates that a single dose delayed release delivery system can be achieved through use of polymeric microparticles formulated from PLGpZS or PLGpS copolymers. In addition as pH changes with matrix erosion can have a deleterious effect on the protein stability it may be advantageous to employ matrices derived from pseudo-serine ester such as PLGpZS or PLGpS wherein there exists some buffering capacity for these changes during the protein release phase.

Example 8

This Example illustrates the immunogenicity of non-proteolytic Hin-47 analog encapsulated or physically mixed with microparticles in mice which were immunized subcutaneously.

To examine the immunogenicity of non-proteolytic Hin-47 analog entrapped in PLG, PLGpZS and PLGpS microparticles formed in accordance with the present invention, groups of five, 6 to 8 week old female BALB/c mice (Charles River Breeding Laboratories, Wilmington, Mass.) were immunized subcutaneously (S.C.) with the following amounts of antigen in 250 μL of PBS (pH 7.4) on days 1 and 35:PLG, PLGpZS and PLGpS microparticles prepared as described in Example 4 containing 0.2 μg or 0.6 μg of non-proteolytic Hin-47 analog (FIG. 8A); and PLG microparticles prepared as described in Example 4 physically mixed with 0.8 μg or 2.5 μg of non-proteolytic Hin-47 analog (FIG. 8B).

The mice showed no gross pathologies or behavioral changes after receiving microparticles that contained encapsulated non-proteolytic Hin-47 analog or microparticles that were physically mixed with non-proteolytic Hin-47 analog. Sera were obtained on days +10, +24, +35, +45 and +60 and were evaluated for the presence of anti-Hin-47 IgG antibodies by antigen specific ELISA. All samples were analyzed in duplicate. Microtiter plate wells were incubated overnight at room temperature with 100 μL of 0.2 μg/mL non-proteolytic Hin-47 analog in 0.05M carbonate-bicarbonate buffer (pH 9.0). The plates were washed with PBS+0.05% Tween 20 (operationally defined as washing buffer). Wells were incubated with 200 μL of 5% skim milk (operationally defined as blocking buffer). After washing with PBS+0.05% Tween 20, the plates were incubated for 1 h at 37° C. with 100 μL of sample serially diluted in blocking buffer. Wells were washed with PBS+0.05% Tween 20 and 100 μL of HRP-conjugated antibody (goat anti-mouse IgG (H+L) (Jackson), sheep anti-mouse IgG1 (Serotec), goat anti-mouse IgG2a (Caltag) or goat anti-mouse IgG2b (Caltag) in blocking buffer was added to each well. After 1 hour incubation at 37° C., the wells were washed five times with PBS+0.05% Tween 20 and 100 μL of freshly prepared colorizing substrate [H₂ O₂ (9 parts) and TMB (1 part)] is added to each well. After 5 minutes incubation in the dark at room temperature the reaction is stopped by adding 50 μL of a 2M H₂ SO₄ solution and the optical density of the fluid in each well was determined at 450 nm using a microplate reader. A normal mouse sera pool was used to establish baseline optical density values in the assay. Hyperimmune mouse Hin-47 antiserum was used as a positive control. Pre-immune sera is used as negative control.

For serum IgA analysis the above procedure was conducted with the following modification. Microtiter plate wells were incubated overnight at room temperature with 100 μL of 1.3 μg/mL non-proteolytic Hin-47 analog in 0.05M carbonate-bicarbonate buffer (pH=9.0), and 100 μL of HRP conjugated rabbit anti-mouse IgA (ZYMED, CA) at 0.06 μg/mL was added to each well.

For secretory IgA analysis the above procedure was conducted with the following modification. 100 μL of HRP conjugated rat anti-mouse IgA (Biotin-Pharmigen) at 0.06 μg/mL was added to each well.

The serum antibody titres following immunization are shown in FIGS. 8A and 8B. The results of immunizations indicate that antigen presented to the immune system entrapped in PLG, PLGpZS or PLGpS microparticles (FIG. 8A) is substantially more immunogenic than soluble antigen at doses sub-optimal to that required with soluble antigen alone. In addition no dose dependence was observed with encapsulated non-proteolytic Hin-47 analog of dose 0.2 μg or 0.6 μg, whereas a marginal increase in titre was found with soluble non-proteolytic Hin-47 analog of dose 0.8 μg or 2.5 μg respectively.

The results of immunizations indicate that antigen presented to the immune system when physically mixed with PLG microparticles (FIG. 8B) is marginally more immunogenic than soluble antigen at similar dose to that given with soluble antigen alone (0.8 μg or 2.5 μg). However, administration of antigen in soluble form or admixed with microparticles elicits a response several orders of magnitude less than that seen for antigen encapsulated within the microparticles demonstrating the advantages of encapsulation over soluble or physically mixing alone.

Interestingly, the IgG subtype profile (FIG. 8C) for pooled serum obtained from the bleeds on day 35 and 60 for microparticle encapsulated non-proteolytic Hin-47 analog, microparticles physically mixed with non-proteolytic Hin-47 analog or soluble non-proteolytic Hin-47 analog shows that by day 35 IgG1 is the dominant subtype with some IgG2b detected irrespective of formulation. By day 60 it is evident that the IgG subtypes induced by non-proteolytic Hin-47 analog encapsulated within microparticles has undergone class switching such that IgG1, IgG2a and IgG2b are more equally represented. The IgG subtypes induced by non-proteolytic Hin-47 analog physically mixed with particles or in soluble form by day 60 is nominally the same as that determined for day 35 with the IgG1 subtype dominant.

Thus, it can be concluded that the qualitative nature of the immune response mediated by microparticles encapsulating antigen is substantially different than that obtained by physically mixing with microparticles or by soluble antigen alone. The presence of IgG2a subtype in the BALB/c mouse model is generally accepted to be indicative of a TH₁ pathway, and IgG1 indicative of a TH₂ pathway. It is evident that via the subcutaneous route the TH₂ pathway is favored for soluble antigen or for antigen physically mixed with microparticles, whereas with antigen encapsulated within microparticles a more balanced TH₁ /TH₂ response is attainable.

Example 9

This Example illustrates the immunogenicity of non-proteolytic Hin-47 analog entrapped in PLG, PLGpZS and PLGpS microparticles formed in accordance with the present invention, in mice immunized intragastrically.

Groups of five, 6 to 8 week old female BALB/c mice (Charles River Breeding Laboratories, Wilmington, Mass.) were immunized intragastrically (I.G.) with the following amounts of antigen in 250 μL of PBS (pH 7.4) on days 1, 7, 14 and 57: PLG, PLGpZS and PLGpS microparticles prepared as described in Example 4 containing 4.0 μg of non-proteolytic Hin-47 analog; and PLG, PLGpZS and PLGpS microparticles prepared as described in Example 4 physically mixed with 4.0 μg non-proteolytic Hin-47 analog (FIG. 9A).

The mice showed no gross pathologies or behavioral changes after receiving microparticles that contained encapsulated non-proteolytic Hin-47 analog or microparticles that were physically mixed with non-proteolytic Hin-47 analog. Sera were obtained on days +13, +35, +56 and +78 and were evaluated for the presence of anti-Hin-47 IgG and IgA antibodies by antigen specific ELISA as described in Example 7.

Sera and intestinal washes were examined for the presence of Hin-47-specific antibodies. To detect and quantify anti-Hin-47 IgG and sIgA in the intestinal lumen, mice were sacrificed by cervical dislocation, their small intestines removed and examined for the presence of antigen-specific antibodies. Individual small intestines were detached from the pyloric sphincter to the caecum and everted over capillary tubes. The everted intestines were incubated in 5 mL of ice cold enzyme inhibitor solution (0.15 M NaCl, 0.01 M Na₂ HPO₄, 0.005 M EDTA, 0.002 M PMSF, 0.05 U/mL Aprotinin, and 0.02% v/v NaN₃) for 4 hours. Intestines were removed and the supernatants clarified by centrifugation (1000×g, 20 minutes) and stored at 0° C. until assayed. Anti-Hin-47 IgG and sIgA titres in samples were determined by Hin-47-specific ELISA as described above but a goat anti-mouse IgA antiserum was used in place of the goat anti-mouse IgG antiserum.

The serum IgG Hin-47-specific antibody titres following I.G. immunization is shown in FIG. 9A. These results indicate that an antigen (non-proteolytic Hin-47 analog) incorporated into PLG, PLGpZS or PLGpS microparticles is substantially more immunogenic than soluble antigen of similar dose (4 μg) and better than antigen that is physically mixed with microparticles when delivered by the intragastric route. It was experimentally determined that a dose of soluble antigen (20 μg) which was five times that which was administered encapsulated within microparticles (4 μg) was required to elicit an essentially equivalent response. This result is atypical for most proteins as there are many examples where in excess of 100 μg of antigen is required to elicit any significant serum IgG antibody response via the intragastric route.

The IgG subtype profile (FIG. 9B) for pooled serum obtained from the bleeds on day 56 and 78 for microparticle encapsulated non-proteolytic Hin-47 analog, microparticles physically mixed with non-proteolytic Hin-47 analog or soluble non-proteolytic Hin-47 analog shows a similar trend as that observed in Example 7. The IgG1 subtype is dominant when antigen is delivered in soluble form or when physically mixed with microparticles. Non-proteolytic Hin-47 analog encapsulated within microparticles exhibits a more balanced profile with IgG1 and IgG2a more equally represented. Thus via the intragastric route with antigen encapsulated within microparticles a more balanced TH₁ /TH₂ response is attainable.

FIG. 9C shows the results for anti-Hin-47 IgA antibody responses obtained from bleeds on day 78. With soluble antigen at 4 μg per dose no detectable serum IgA was found, however at 20 μg per dose a few responders were observed. A single significant response was observed with antigen encapsulated within PLG microparticles and moderate responses observed for antigen encapsulated within PLGpZS or PLGpS microparticles. Similarly modest response is seen for antigen physically mixed with PLG, PLGpZS or PLGpS microparticles. The highest average levels of serum IgA were obtained for antigen encapsulated within PLGpS microparticles.

The intestinal lavage conducted on day 78 revealed minimal levels of IgG or sIgA specific for Hin-47 analog in the mucosal secretions obtained from non-proteolytic Hin-47 analog encapsulated within PLG, PLGpZS or PLGpS microparticles. This is likely due to the very low levels of encapsulated antigen administered in this experiment (4 μg per dose) as oral doses of antigen ranging from 30 μg to 100 μg are usually required to elicit a significant mucosal response in the absence of any other mucosal adjuvants.

Example 10

This Example illustrates the immunogenicity of non-proteolytic Hin-47 analog entrapped in PLG, PLGpZS and PLGpS microparticles formed in accordance with the present invention, in mice immunized intranasally.

Groups of five, 6 to 8 week old female BALB/c mice (Charles River Breeding Laboratories, Wilmington, Mass.) were immunized intranasally (I.N.) with the following amounts of antigen in 25 μL of PBS (pH 7.4) on days 1, 7, 14 and 57: PLG, PLGpZS and PLGpS microparticles prepared as described in Example 4 containing 4.0 μg of non-proteolytic Hin-47 analog; and PLG, PLGpZS and PLGpS microparticles prepared as described in Example 4 physically mixed with 4.0 μg non-proteolytic Hin-47 analog (FIG. 10A).

The mice showed no gross pathologies or behavioral changes after receiving microparticles that contained encapsulated non-proteolytic Hin-47 analog or microparticles that were physically mixed with non-proteolytic Hin-47 analog. Sera were obtained on days +13, +35, +56 and +78 and were evaluated for the presence of anti-Hin-47 IgG and IgA antibodies by antigen specific ELISA as described in Example 7.

Sera and lung lavage washes were examined for the presence of Hin-47-specific antibodies. To detect and quantify anti-Hin-47 IgG and sIgA in the respiratory tract, mice were sacrificed by cervical dislocation, a small incision was made in the trachea and a tube inserted through the trachea into the lungs where 400 μL of an enzyme inhibitor solution (0.15 M NaCl, 0.01 M Na₂ HPO₄, 0.005 M EDTA, 0.002 M PMSF, 0.05 U/mL Aprotinin, and 0.02% v/v NaN₃) was injected. This solution was then withdrawn, placed on ice and the supernatants clarified by centrifugation (1000×g, 20 minutes) and stored at 0° C. until assayed. Anti-Hin-47 IgG and sIgA titres in samples were determined by Hin-47-specific ELISA as described in Example 7.

The serum IgG Hin-47-specific antibody titres following I.N. immunization is shown in FIG. 10A. These results indicate that an antigen (non-proteolytic Hin-47 analog) incorporated into or physically mixed with PLG, PLGpZS or PLGpS microparticles is more immunogenic than soluble antigen of similar dose (4 μg). Essentially equivalent response was obtained for antigen that is encapsulated or physically mixed with microparticles by the intranasal route.

The IgG subtype profile (FIG. 10B) for pooled serum obtained from the bleeds on day 56 and 78 for microparticle encapsulated non-proteolytic Hin-47 analog, microparticles physically mixed with non-proteolytic Hin-47 analog or soluble non-proteolytic Hin-47 analog illustrates a trend different from that shown in Example 7 or Example 8. Non-proteolytic Hin-47 analog encapsulated within microparticles exhibits a more balanced profile with IgG1, IgG2a and IgG2b essentially equally represented at either timepoint (day 56 or day 78). For antigen delivered in soluble form or when physically mixed with microparticles, a similar profile is seen by day 78 where significant levels of IgG2a can also be seen.

Thus, via the intranasal route, the TH₁ /TH₂ response is essentially the same irrespective of whether antigen is encapsulated within microparticles, physically mixed with microparticles or in soluble form.

FIG. 10C shows the results for anti-Hin-47 IgA antibody responses obtained from bleeds on day 78. With soluble antigen no detectable serum IgA was found. However, significant response is seen for antigen that is encapsulated or physically mixed with microparticles. The highest levels obtained for antigen either encapsulated or physically mixed with PLGpS microparticles.

The lung lavage conducted on day 78 revealed substantial differences with respect to IgG and sIgA detected from secretions. The anti-Hin-47 IgG antibody response (FIG. 10D) from soluble antigen was negligible, however antigen encapsulated within microparticles or physically mixed with PLG microparticles elicited significant levels of IgG from half of each group examined. The most reproducible response for IgG was found with antigen physically mixed with microparticles derived from PLGpZS or PLGpS where most or all mice examined possessed significant levels of IgG.

The anti-Hin-47 sIgA antibody response (FIG. 10E) was similar to that obtained for IgG in FIG. 10D. Soluble antigen response was negligible with antigen encapsulated within microparticles or physically mixed with PLG microparticles showing some response. The most significant response for sIgA was found with antigen physically mixed with microparticles derived from PLGpZS or PLGpS where most mice have reasonable levels of sIgA.

The induction of local protection at mucosal surfaces is often associated with the presence IgG and sIgA in local secretions. Whereas it cannot be ruled out that the intranasal immunization has not also resulted in immunization of the upper respiratory tract, it is clear that for serum IgG antibody response encapsulated or physically mixed antigen with microparticles is effective. To induce local secretions of IgG and sIgA physically mixing antigen with microparticles and more specifically microparticles formulated from either PLGpZS or PLGpS appears to be the more suitable method under these conditions.

Example 11

This Example illustrates the immunogenicity of Flu-X-31 or Flu X-31 plus a co-adjuvant BAY R1-005 entrapped in PLG, PLGpZS and PLGpS microparticles formed in accordance with the present invention, in mice immunized subcutaneously.

Groups of six, 6 to 8 week old female BALB/c mice (Charles River Breeding Laboratories, Wilmington, Mass.) were immunized subcutaneously (S.C.) with the following amounts of antigen in 250 μL of PBS (pH 7.4) on day 1: PLG, PLGpZS and PLGpS microparticles prepared as described in Example 4 containing 5.0 μg of Flu X-31 (1.5 μg HA) or 5.0 μg of Flu X-31 (1.5 μg HA) and 50 μg BAY R1-005 when administered in soluble form or approximately 20 μg BAY R1-005 when co-encapsulated (FIG. 11).

The mice showed no gross pathologies or behavioral changes after receiving microparticles that contained encapsulated Flu X-31 or Flu X-31 with BAY R1-005. Sera were obtained on days +21 and +33 and were evaluated for the presence of anti-Flu X-31 IgG antibodies by antigen specific ELISA. All samples were analyzed in duplicate.

Microtiter plate wells were incubated overnight at room temperature with 500 μL of 4.0 μg/mL Flu X-31 in 0.05M carbonate-bicarbonate buffer (pH=9.6). The plates were washed with PBS+0.05% Tween 20 (operationally defined as washing buffer). Wells were incubated with 200 μL of 5% skim milk (operationally defined as blocking buffer). After washing with PBS+0.05% Tween 20, the plates were incubated for 1 h at 37° C. with 100 μL of sample serially diluted in blocking buffer. Wells were washed with PBS+0.05% Tween 20 and 100 μL of HRP-conjugated antibody (goat anti-mouse IgG (H+L), IgG1, IgG2a or IgG2b) in blocking buffer was added to each well. After 1 hour incubation at 37° C., the wells were washed 5× with PBS+0.05% Tween 20 and 100 μL of freshly prepared colorizing substrate [H₂ O₂ (9 parts) and TMB (1 part)] is added to each well. After 5 minutes incubation in the dark at room temperature the reaction is stopped by adding 50 μL of a 2M H₂ SO₄ solution and the optical density of the fluid in each well was determined at 450 nm using a microplate reader. A normal mouse sera pool was used to establish baseline optical density values in the assay. Hyperimmune mouse Flu X-31 antiserum was used as a positive control. Pre-immune sera is used as negative control.

The serum antibody titres following immunizations are shown in FIG. 11. The results of a single immunization (day 1) indicate that antigen presented to the immune system entrapped in PLG, PLGpZS or PLGpS microparticles is more immunogenic than soluble antigen alone. The most relevant results were obtained with Flu X-31 or Flu X-31 plus BAY R1-005 encapsulated within PLGpZS microparticles. Although a sub-optimal dose of BAY R1-005 was encapsulated within all microparticles examined, the immunogenic response with the PLGpZS microparticles also proved to be significantly higher than that obtained with soluble Flu X-31 and BAY R1-005 alone.

The studies presented in this Example demonstrate that viral antigens from influenza virus can be made more immunogenic and elicit high levels of serum IgG antibodies, when the antigens are entrapped in microparticles formed in accordance with the present invention. In addition the significantly higher immunogenicity displayed by the microparticle systems after a single immunization demonstrates the potential of these materials for development as single dosage vaccines.

Example 12

This Example illustrates the immunogenicity of Flu-X-31 or Flu X-31 plus a co-adjuvant BAY R1-005 entrapped in PLG, PLGpZS and PLGpS microparticles formed in accordance with the present invention, in mice immunized intranasally.

Groups of six, 6 to 8 week old female BALB/c mice (Charles River Breeding Laboratories, Wilmington, Mass.) were immunized intranasally (I.N.) with the following amounts of antigen in 25 μL of PBS (pH 7.4) on days 1 and 34: PLG, PLGpZS and PLGpS microparticles prepared as described in Example 4 containing 5.0 μg of Flu X-31 (1.5 μg HA) or 5.0 μg of Flu X-31 (1.5 μg HA) and 50 μg BAY R1-005 when administered in soluble form or approximately 20 μg BAY R1-005 when co-encapsulated (FIG. 12).

The mice showed no gross pathologies or behavioral changes after receiving microparticles that contained encapsulated Flu X-31 or Flu X-31 with BAY R1-005. Sera were obtained on days +21, +33 and +92 and were evaluated for the presence of anti-Flu X-31 IgG antibodies by antigen specific ELISA as described in Example 10. All samples were analyzed in duplicate.

Mice immunized I.N. with soluble antigen, soluble antigen plus co-adjuvant or encapsulated antigen showed a similar anti-Flu X-31 IgG antibody response. Interestingly, a suppressed (likely due to delayed release) immunogenic response for encapsulated antigen plus co-adjuvant relative to soluble antigen, antigen plus adjuvant or encapsulated antigen on day +21 and +33 was shown when administered via the nasal route. However, after the second immunization (day 34) a significant boost in response with these groups was observed resulting in essentially similar immunogenicity on day +92 for all groups irrespective of adjuvant used.

The results of the I.N. immunizations described in this example shows that the immunogenicity of an antigen or antigen plus a co-adjuvant cannot be significantly enhanced by entrapment in microparticles formed in accordance with the present invention.

Example 13

This Example illustrates the immunogenicity of Flu A-Texas or Flu A-Texas+BAY R1-005 encapsulated or physically mixed with microparticles in mice immunized subcutaneously.

It is known that most non-replicating viral vaccines require multiple doses for sufficient serum antibody titres to be protective. Thus, it is strongly desirable to achieve this by administering a single dose of antigen.

We sought to examine the immunogenicity of Flu A-Texas or Flu A-Texas plus a co-adjuvant BAY R1-005 which was entrapped in PLGpS microparticles or physically mixed with microparticles administered as a single dose, formed in accordance with the present invention. Groups of six, 6 to 8 week old female DBA2 mice (Charles River Breeding Laboratories, Wilmington, Mass.) were immunized subcutaneously (S.C.) with the following amounts of antigen in 250 μL of PBS (pH 7.4) on day 1: PLGpS prepared as described in Example 4 containing 1.0 μg of Flu A-Texas (0.35 μg HA) or 10.0 μg of Flu A-Texas (3.5 μg HA) or 1.0 μg of Flu A-Texas (0.35 μg HA) and approximately 2.0 μg of BAY R1-005 or 10.0 μg of Flu A-Texas (3.5 μg HA) and approximately 20 μg of BAY R1-005 or microparticles prepared as described in Example 4 physically mixed with 1.0 μg of Flu A-Texas (0.35 μg HA) and 20 μg of BAY R1-005 or 10.0 μg of Flu A-Texas (3.5 μg HA) and 20 μg of BAY R1-005 (FIG. 19).

The core loading of PLGpS microparticles containing Flu A-Texas and BAY R1-005 was determined via amino acid analysis (FIG. 12). The mass of microparticles administered was adjusted such that the required dose of Flu A-Texas (1.0 μg of Flu A-Texas (0.35 μg HA) for the low dose groups or 10.0 μg of Flu A-Texas (3.5 μg HA) for the high dose groups) was delivered. Thus the dose of BAY R1-005 delivered for the high dose groups is ten fold greater than that of the low dose groups examined. It is expected that formulation conditions can be adjusted such that the quantity of BAY R1-005 co-encapsulated is comparable.

The mice showed no gross pathologies or behavioral changes after receiving microparticles that contained encapsulated Flu A-Texas or Flu A-Texas with BAY R1-005. Sera were obtained on days +21 and +42 and were evaluated for the presence of functional antibody via the hemagglutination inhibition antibody assay (HAI). All samples were analyzed in duplicate.

The influenza hemagglutination inhibition antibody assay was performed with heat-inactivated mouse serum that had been incubated for 30 minutes with 10% chicken red blood cells to remove non-specific inhibitors. Twofold dilutions of sera were added to a 96 well microtiter plate and 8 HA units of virus suspension in an equal volume were added to each well and incubated at room temperature for 30 minutes. A 1.0% suspension of chicken red blood cells were added to each well and incubated at room temperature for 30 minutes. Positive and negative reference sera are included in the test to ascertain specificity and sensitivity of the test. Positive sera from influenza virus immunized animals. Negative sera from PBS immunized animals, titre should be less than or equal to 15. The HAI titres are expressed as the reciprocal of the highest dilution that completely inhibits hemagglutination of erythrocytes.

The results of a single immunization (day 1) is shown in FIG. 19 and indicates that by day +42 antigen presented to the immune system in soluble form or entrapped in PLGpS microparticles elicits negligible or low functional antibody. Antigen presented by physically mixed with BAY R1-005 (10 μg Flu A-Texas dose response is eight times that of soluble antigen) or with PLGpS microparticles (1 μg Flu A-Texas dose response is six times that of soluble antigen, 10 μg Flu A-Texas dose response is sixteen times that of soluble antigen) elicited moderate functional antibody response which proved slightly better for antigen that was physically mixed with PLGpS microparticles. This was especially true for the lower 1 μg Flu A-Texas dose administered. In each case a dose dependence was observed. The most relevant results were obtained with Flu A-Texas plus BAY R1-005 encapsulated within PLGpS microparticles (1 μg Flu A-Texas dose response is eight times that of soluble antigen, 10 μg Flu A-Texas dose response is sixty four time that of soluble antigen). The completely physically mixed system of Flu A-Texas plus PLGpS microparticles plus BAY R1-005 provided a moderate increase relative to the soluble antigen controls (eight times that of soluble antigen irrespective of whether the dose of Flu A-Texas administered was 1 μg or 10 μg).

The studies presented in this Example demonstrate that viral antigens from influenza virus elicit high levels of functional antibodies when the antigens are entrapped in microparticles in the presence of an additional adjuvant (as determined by HAI titres), formed in accordance with the present invention. There is a dose dependence observed and in addition the significantly higher functional antibody (a correlate for protection) displayed by the microparticle antigen and adjuvant co-encapsulated systems after a single immunization further demonstrate the potential of these materials for development as single dosage forms.

SUMMARY OF THE DISCLOSURE

In summary of this disclosure, the present invention provides a particulate carrier for an agent, particularly one having biological activity, comprising a matrix of polymer and biologically active material. The particulate carriers in the form of microparticles are able to efficiently deliver agents to the cells of the immune system of a subject following mucosal or parenteral administration to produce an immune response. Modifications are possible within the scope of this invention.

                  TABLE 1                                                          ______________________________________                                         Antigen(s) entrapped in                                                        PLG,                                                                           PLGpZS or PLGpS                                                                microparticles     Antigen Preparation                                         ______________________________________                                         Hin-47 (1.55 mg/mL) +                                                                             800 μL of Hin-47 in                                      BAY (5.0 mg/mL)    aqueous internal phase                                                         plus 40.0 mg of BAY in                                                         the organic phase                                           rD-15 (2.05 mg/mL) 800 μL of rD-15.                                         Hin-47 (1.95 mg/mL) +                                                                             400 μL of Hin-47 plus 400                                rD-15 (1.95 mg/mL) μL of rD-15.                                             Flu X-31 (2.0 mg/mL)                                                                              800 μL of Flu X-31 or 800                                Flu A-Texas (1.48 mg/mL)                                                                          μL of Flu A-Texas                                        Flu (2.0 mg/mL) +  800 μL of Flu X-31 or 800                                BAY (5.0 mg/mL)    μL of Flu A-Texas in                                     Flu A-Texas (1.48 mg/mL)                                                                          aqueous internal phase                                      +                  plus 40.0 mg of BAY in                                      BAY (5.0 mg/mL)    the organic phase                                           ______________________________________                                    

                  TABLE 2                                                          ______________________________________                                         Summary of Microparticle                                                       Core Loading and Encapsulation Efficiencies                                    (Hin-47, Hin-47 + Bay R1-005)                                                                   Epitope                                                                        Equiv.   Total        Total                                                    Hin-47 via                                                                              Protein                                                                               Epitope                                                                              Adjuvant                                Protein          ELISA.sup.1                                                                             via AAA.sup.2                                                                         vs Total                                                                             via AAA.sup.2                           (Conc.)          (Encap.  (Encap.                                                                               Protein                                                                              (Encaps.                                (Adjuvants)                                                                            Polymer  Eff.).sup.3                                                                             Eff.).sup.3                                                                           %     Eff.).sup.3                             ______________________________________                                         Hin-47  PLG      1.4 ug/mg                                                                               2.8 ug/mg                                                                             50%                                           (1.55            (10.2%)  (20.4%)                                              mg/mL)  PLGpZS   5.3 ug/mg                                                                               7.5 ug/mg                                                                             71%                                                            (30.8%)  (43.5%)                                                      PLGpS    1.6 ug/mg                                                                               3.3 ug/mg                                                                             48%                                                            (11.6%)  (23.9%)                                              Hin-47  PLG      2.5 ug/mg                                                                               3.8 ug/mg                                                                             66%   13.5 (3.4%)                             (1.55            (20.1%)  (30.6%)                                              mg/mL)  PLGpZS   4.1 ug/mg                                                                               5.5 ug/mg                                                                             75%   15.6 (3.9%)                             Bay-R1005        (19.8%)  (26.6%)                                              (5.0    PLGpS    6.1 ug/mg                                                                               9.2 ug/mg                                                                             66%   23.2 (4.6%)                             mg/mL)           (39.4%)  (59.4%)                                              ______________________________________                                          .sup.1) ELISA values are averages of 2 independent measurements of protei      obtained after complete hydrolysis of microparticles.                          .sup.2) AAA values are averages of 2 independent measurements on protein       (or adjuvant) encapsulated within microparticles and 2 independent             measurements on protein (or adjuvant) obtained after complete hydrolysis       of microparticles.                                                             .sup.3) Encapsulation efficiency (Encap. Eff.) calculated as follows:          total mass of protein (or adjuvant) recovered × 100% total amount o      protein (or adjuvant) used                                               

                  TABLE 3                                                          ______________________________________                                         Summary of Microparticle                                                       Core Loading and Encapsulation Efficiencies                                    (rD-15, rD-15 + Hin-47)                                                                           Epitope Equivalent                                                                          Total Protein                                  Protein            Hin-47 via ELISA.sup.1                                                                      via AAA.sup.2                                  (Conc.)  Polymer   (Encaps. Eff.).sup.3                                                                        (Encaps. Eff.).sup.3                           ______________________________________                                         rD-15    PLG                     7.8 ug/mg (43.7%)                             (1.95 mg/mL)                                                                            PLGpZS                  7.1 ug/mg (39.2%)                                      PLGpS                   7.3 ug/mg (43.7%)                             rD-15    PLG       1.6 ug/mg (8.0%)                                                                             7.0 ug/mg (35.1%)                             (1.95 mg/mL)                                                                            PLGpZS    5.5 ug/mg (26.1%)                                                                           13.1 ug/mg (62.1%)                             + Hin-47 PLGpS     2.4 ug/mg (10.8%)                                                                           11.6 ug/mg (52.1%)                             (1.95 mg/mL)                                                                   ______________________________________                                          .sup.1) ELISA values are averages of 2 independent measurements of protei      obtained after complete hydrolysis of microparticles.                          .sup.2) AAA values are averages of 2 independent measurements on protein       encapsulated within microparticles and 2 independent measurements on           protein obtained after complete hydrolysis of microparticles.                  .sup.3) Encapsulation efficiency (Encaps. Eff.) calculated as follows:         total mass of protein recovered × 100% total amount of protein used

                  TABLE 4                                                          ______________________________________                                         Summary of Microparticle Core Loadings and                                     Encapsulation Efficiencies for Flu X-31, Flu X-31 + Bay R1-005                 and Flu A-Texas, FIu A-Texas + BAY R1-005                                      Protein            Total Protein                                                                               Total Adjuvant                                 (Conc.)            via AAA.sup.1                                                                               via AAA.sup.1                                  (Adjuvants)                                                                             Polymer   (Encaps. Eff.).sup.2                                                                        (Encaps. Eff.).sup.2                           ______________________________________                                         Flu X-31 PLG       4.7 ug/mg (26.1%)                                           (2.0 mg/mL)                                                                             PLGpZS    6.1 ug/mg (34.1%)                                                    PLGpS     7.1 ug/mg (39.7%)                                           Flu X-31 PLG       5.6 ug/mg (35.1%)                                                                           22.9 ug/mg (5.2%)                              (2.0mg/mL)                                                                              PLGpZS    8.4 ug/mg (52.5%)                                                                           28.1 ug/mg (10.0%)                             Bay-R1005                                                                               PLGpS     5.0 ug/mg (31.0%)                                                                           27.4 ug/mg (8.4%)                              (5.0 mg/mL)                                                                    Flu A-Texas                                                                             PLGpS     2.7 ug/mg (22.8%)                                           (1.48 mg/mL)                                                                   Flu A-Texas                                                                             PLGpS     3.4 ug/mg (31.6%)                                                                           11.5 ug/mg (3.5%)                              (1.48 mg/mL)                                                                   Bay-R1005                                                                      (5.0 mg/mL)                                                                    ______________________________________                                          .sup.1) AAA values are averages of protein (or adjuvant) isolated after        complete hydrolysis of microparticles and protein (or adjuvant)                encapsulated within microparticles.                                            .sup.2) Encapsulation efficiency (Encaps. Eff.) calculated as follows:         total mass of protein (or adjuvant) recovered × 100% total amount o      protein (or adjuvant) used                                               

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30. Wiesmuller, Vaccine, 8, 1989, 29. 

What we claim is:
 1. A biodegradable, biocompatible polymer having a molecular weight of about 5,000 to about 40,000 daltons and having the general formula: ##STR3## wherein: R₁, R₂, and R₅ are selected independently and are selected from H, linear or branched alkyl groups;R₃ and R₄ are H; R₆ is selected from H, an amine protecting group, a spacer molecule or a biologically active species; X is selected from an O or S group; and x and y are integers such that at least about 95% of the polymer is comprised of α-hydroxy acid residues.
 2. The polymer of claim 1 which is derived by copolymerization of monomers comprising at least one α-hydroxy acid and at least one α-amino acid.
 3. The polymer of claim 2, wherein the at least one α-hydroxy acid has the formula R₁ R₂ COHCO₂ H, wherein the R₁ and R₂ groups are H, linear or branched alkyl units, the alkyl unit being represented by the formula C_(n) H_(2n+1), where n=integer of about 1 to
 10. 4. The polymer of claim 3, wherein the α-hydroxy acids comprise a mixture of α-hydroxy acids, one of said mixture of α-hydroxy acids having R₁ and R₂ groups which are hydrogen and the other of said mixture of α-hydroxy acids having an R₁ group which is CH₃ and R₂ group which is H.
 5. The polymer of claim 2, wherein the at least one α-amino acid has the formula R₅ CHNHR₆ CO₂ H, wherein the R₅ group is a hydroxyl methyl or methyl thiol group and R₆ is an amine protecting group.
 6. The polymer of claim 5, wherein the amine protecting group is selected from the group consisting of carbobenzyloxy (CBZ or Z), benzyl (Bn), para-methoxybenzyl (MeOBn), benzyloxymethoxy (BOM), tert-butyloxycarbonyl (t-BOC) and [9-fluorenylmethyl oxy]carbonyl (FMOC).
 7. The polymer of claim 2, wherein the at least one α-hydroxy acid is selected from the group consisting of L-lactic acid, D,L-lactic acid, glycolic acid, hydroxy valeric acid and hydroxybutyric acid.
 8. The polymer of claim 2, wherein the at least one amino acid is serine.
 9. The polymer of claim 1, wherein said polymer is poly-D,L-lactide-co-glycolide-co-pseudo-Z-serine ester (PLGpZS).
 10. The polymer of claim 1, wherein said polymer is poly-p,L-lactide-co-glycolide-co-pseudo-serine ester(PLGpS).
 11. The polymer of claim 1, wherein R₆ is at least one biologically active species.
 12. The polymer of claim 11, wherein R₆ is at least one spacer molecule to which at least one biologically active species is coupled.
 13. A biodegradable, biocompatible polymer having a molecular weight of about 5,000 to about 40,000 daltons and having the general formula: ##STR4## wherein: R₁, R₂, and R₅ are selected independently and are selected from H, linear or branched alkyl groups;R₃ and R₄ are H; R₆ is selected from H, an amine protecting group, a spacer molecule or a biologically active species; X is selected from an O or S group; and x and y are integers such that at least about 95% of the polymer is comprised of α-hydroxy acid residues, the spacer molecule being selected from α-hydroxy acids represented by the formula:

    R.sub.7 R.sub.8 COHCOH

wherein the R₇ or R₈ groups are independently H, linear or branched alkyl units and α-amino acids represented by the formula:

    R.sub.9 CHNHR.sub.10 CO.sub.2 H

wherein the R₉ group is a hydroxyl methyl or methyl thiol group and R₁₀ is an amine protecting group.
 14. The polymer of claim 11, wherein the at least one biologically active species is selected from the group consisting of cell bioadhesion groups, macrophage stimulators, poly amino acids and polyethylene glycol. 